


Quantum Physics

by shorelines



Category: Undertale (Video Game)
Genre: Gen, Gender-Neutral Frisk, Post-Pacifist Route, i am not an astrophysicist
Language: English
Status: Completed
Published: 2015-11-26
Updated: 2015-11-26
Packaged: 2018-05-03 10:39:12
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,093
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/5287505
Author URL: https://archiveofourown.org/users/shorelines/pseuds/shorelines
Summary: <blockquote class="userstuff">
              <p>Frisk and Sans go to an observatory. There are particles, and then there are waves.</p>
            </blockquote>





	Quantum Physics

"You tricked me!" Frisk giggled, and they rubbed at the pink ink on their eye.

"I gotcha, kiddo!" Sans said, grinning. He leaned against the rocky wall as Frisk blinked rapidly. "There aren't any real stars down here."

Frisk wiped their hands on their striped shirt. "Sans, have you ever seen a real star?"

Sans shook his head. "I've just heard what the older monsters have said — that Waterfall's the closest night sky we've got."

Water rushed somewhere farther down the cavern as the kid grew quiet. Sans put his hands in his pockets and waited, watching determination come over Frisk's face.

"I'm going to get the monsters out," Frisk said suddenly, their face solemn. "Then, I am going to take you to outer space."

Sans laughed. "Thanks, kid, that means a lot. The barrier is pretty strong, but I don't blame you for trying."

In this world, Frisk is successful. In the years after the monsters are freed, there was much work to be done, but Frisk never forgot what they said to Sans that day.

* * *

"So it turns out that even for the ambassador between monsters and humans, space travel is pretty expensive," Frisk said, casually. They had just returned from school, and Sans almost spat out his pop drink all over Toriel's sofa. "So it looks like no outer space for you."

"I think I like better it on the ground anyway," Sans said, and Frisk hopped over the back of the sofa. "You remember?"

"I don't break my promises, Sans," Frisk said, wagging a finger. "I might not be able to launch you into space, but I have got the next best thing."

The look of intent determination on their face was enough to make Sans sweat. "What is it?"

"You know that joint effort human-monster observatory being built? I get private access for one night, before it goes public." Frisk smiled and bounced on the sofa a little. "After all, being ambassador has _some_ perks. I was wondering… do you want to come with me?"

"I'd love to," said Sans, pleasantly surprised. "When are we going?"

"Nice!" Frisk cheered, and they clapped their hands. "The night of the meteor shower, I was thinking. Unless you want to —?"

"Sounds perfect." Sans grinned and ruffled Frisk's hair. "I hope you know how to operate all that high-tech machinery without breaking it."

"I might be in high school, but I was accepted into that advanced astrophysics class for a reason, Sans! You'll see."

He did see. On one cool summer night, Frisk drove them up Mount Ebott to the observatory. More than once, Sans noticed Frisk glance at the general direction of the spot where they had first fallen down. Inexplicably, once the last monster had exited the underground all those years ago, the tunnels had just collapsed. Every entrance and exit was sealed, and the monsters truly could not go back.

Sans had a feeling that Frisk had wanted to, very much. For what, he never knew.

"Hey, does this observatory have a name yet, Frisk?" asked Sans.

Frisk stiffened, just slightly. "Yeah. I named it."

"So… what's it called?"

"The Asriel Observatory."

Sans glanced at Frisk, but their eyes were firmly on the road. "After Toriel and Asgore's son?"

Frisk didn't answer for so long that Sans thought they were ignoring him. Then, so quietly that Sans barely heard it, "The only one I couldn't save," Frisk murmured.

"H-hey, don't blame yourself. You weren't there."

Frisk only pressed their lips together and nodded tightly. They cast another glance out the window.

The car cleared the trees, and Sans could see the observatory, silhouetted against a clear, starry sky. Frisk carefully parked the car, and when Sans got out, he saw it was a perfect parking job. "Looks like those lessons with Papyrus are paying off."

Frisk grimaced. "I think I just learn what to avoid when I go driving with him. He always insists I go faster."

Sans hummed as Frisk fished for their phone. "Don't tell Toriel that, or she will never let Papyrus near a car again." Frisk found their phone, and the keyring had a shiny plastic card attached to it.

"Fancy, isn't it?" Frisk said as they swiped the keycard on the door. They pushed it open, and as they entered, the lights of the observatory flickered on, one by one.

It was a magnificent facility. Glowing charts lined the walls, and the lights of the new computer terminals blinked red and blue and green. There were two more doors, presumably leading into the other rooms of the space centre. At the center of the circular room, however, was an enormous, gleaming white telescope, complete with a spiral staircase leading up to it.

"This is incredible, Frisk," Sans said softly, padding inside. Frisk closed the door behind them with a click. "Now I'm a little jealous that we only get one night here."

Frisk chuckled and. "You can come back as often as you like, Sans. But come on! There's so much to see before the meteor shower begins." They skipped over to one of the computer terminals, swiped the keycard, and began typing. With a groan, the curved main shutter began to open. In that growing rectangle, Sans saw the clear night sky, the stars unobstructed by city smog up here on Mount Ebott.

"Climb up those steps to the telescope and put your eye socket up against the lens," Frisk said, glancing over at Sans. They typed something else, and the telescope began to move.

"There isn't any ink on it, is there?" Sans asked as he ascended the steps.

Frisk laughed. "That thing is worth millions of dollars and is a monument to the peaceful relations between humans and monsters. I wouldn't dare."

"Alright, kiddo, I trust you." Sans leaned forward and looked through the telescope. A world of swirling galaxies and red and blue stars shimmered above him, and Sans couldn't stop a small gasp from escaping. He had had to leave his own telescope underground, and these were the real stars he'd been missing.

"Do you see that triangle of stars?" Frisk asked. He could hear the smile in their voice. "That's the Summer Triangle: Deneb, Altair, and Vega." Sans nodded, and Frisk typed something else. The telescope whirred again, and while it barely moved, his field of vision did. "To its right is the Big Dipper."

"What are you typing to move the telescope, kiddo?" Sans asked, as he picked out the brightest stars that formed the constellation.

"Right ascension and declination. They're like coordinates, but for space," Frisk said. "My astrophysics teacher taught it to me."

"I'm glad you're here, then." For all his knowledge of quantum physics, Sans didn't know this.

As if they could read his mind, Frisk said, "You know, I didn't realize what the quantum physics textbooks between the joke books in your old house really meant for a long time. I just thought you were being silly."

Sans leaned back from the telescope, and saw Frisk staring at him intently. "It was silly, kiddo. All of that — it was useless."

"It seemed to me like you were successful. That machine… it worked, didn't it?"

Sans shrugged. "People got hurt, kiddo. One, very badly. It was worse than useless."

"I don't think anything is ever useless. That's not what physics says."

"Do you know what else physics says? Nothing is ever truly lost, even the things that have died, even the things we can't quite remember. So…" Sans closed his eyes and opened them. "D i d  y o u  s e e  h i m ?"

"The man who speaks in hands?" Frisk wasn't fazed. They rarely were, these days. "Yes. Just once, briefly. Sans… what happened to him?"

Sans sighed. "That's a story for another time, kiddo."

"Would you tell it to me, one day?"

"One day," Sans said, and he smiled a little. "Maybe after you take a quantum physics class."

To his relief, Frisk laughed and turned back to the computer. "Well, that's fair. I still have more I want to show you." The telescope shifted slightly, and Sans looked back into the lens. His field of vision had moved again, and in fact, was closing in one something. Sans realized what it was once the rings came into view.

"Saturn?" he said, and Frisk tapped once, and the zooming stopped. Oh, it was incredible, vast and all light and shadow. "I've only ever seen pictures."

"I want to show you Polaris, too," said Frisk, and the circle of space zoomed out again. Saturn got smaller and smaller, and Sans felt as if he were falling away from it. Then the telescope focused on a bright star. "It's my favourite, even though it's just the North Star."

"What about Sirius?" Sans asked.

"We can't see Sirius in the summertime from where we are."

"That is a _serious_ shame."

Frisk laughed, as they always did at his terrible jokes. "We have to head outside. I think the meteor shower will start soon."

Sans reluctantly pulled away from the telescope, but he didn't want to miss what they had come here for. Frisk was already by the door by the time Sans descended the telescope stairs.

Outside, Sans could see the constellations Frisk had pointed out to him — just all at once. There was the Summer Triangle, and there was Saturn, as a tiny speck. Frisk took his hand and led him to the open lawn next to the observatory. They smiled down at him, and Sans was reminded that Frisk was a head taller than him now. They had grown up so quickly in the years since he met them. Frisk sat them down at a soft spot of grass, the summer night both warm and cool.

"I think the observatory will be a big hit," said Sans, zipping up his hoodie. "The kids will love it."

Frisk didn't answer, but their hands were folded tightly in their lap. They had gone quiet still. "Sans, are you still afraid of me?"

Sans turned his head away, and wondered if the stars could see a blue light shining back at them. He willed it away, and turned back to Frisk. "You don't easily forget what I've seen. And you still have the power."

"Well, I am still afraid of you. So that makes two of us."

Sans didn't apologize, and neither did Frisk. This push and pull was something they had learned to live with, over the years. It didn't stop them from loving each other, but some nights were harder than others.

"After I am dead, and the timelines settled, will you tell the others what they missed?"

"Never. Not even if I live a thousand years."

Frisk glanced at him. "Monsters live that long?"

"Nah," Sans grinned, but he couldn't bring himself to reach out to Frisk, ruffle their hair like he usually did. "I'm just messing with ya."

"I wish I could have shown you my favourite constellation today," said Frisk, looking up at the stars. The Milky Way streamed above them, a gaseous arc across the clear sky. "The constellation Gemini. The Twins, Castor and Pollux."

Sans hummed. "Maybe we can come back, when the time is right."

"When the time is right," Frisk agreed. Then, something bright winked in the sky. "Oh, it's starting!"

Frisk was right. One, then another meteor streaked across the sky, bright and white. More and more filled the sky, streaks criss-crossing over the stars. If Sans had felt like he was falling from the stars before, this made him feel as if the stars were coming to him.

"The Perseids," Frisk whispered, and Sans nodded, awestruck. "All debris from a passing comet, burning up before they hit the surface of the Earth."

"And if they do make it to the surface?"

"Then they are called meteorites, and they are bright and new and strange and different. But, they are wonderful."

Sans smiled, and held out his hand. Frisk took it, and they watched the meteor storm for hours.

Some nights were hard, and tonight, it was no different. What Sans and Frisk knew would never make their friendship easy, but he couldn't imagine life without them — without someone else who understood.

Physics says that this may very well be one of an infinite number of universes. But Sans was grateful he lived in this one, with this Frisk. He hoped they knew that.

Sans held their hand gently, and Frisk held onto his. 

**Author's Note:**

> 1\. I have no idea how an observatory works.
> 
> 2\. This is set sometime during the summer months, somewhere in the northern hemisphere. Some of the astronomy is probably wrong, but I tried my best.
> 
> 3\. When they are talking about nothing ever being truly lost, they are referring to the law of conservation of energy.
> 
> 4\. The Perseids aren't as intense in real life, but they're still pretty cool.


End file.
